1. Field of the Invention
This invention pertains to devices used to connect a single subscriber telephone line to voice, data modem, and facsimile devices
2. Description of the Prior Art
Prior art provides numerous, but incomplete methods to connect voice, data modem, and facsimile equipment to a single subscriber telephone line. The most common form of the prior art connect only fax and voice to a single subscriber line and do not process data modem calls. In all instances of prior art, proper switching of the line to voice, fax, and data modem equipment requires special subscriber line services such as distinctive ring or human intervention on the calling or receiving end to properly distinguish between voice, data modem, and facsimile calls. In some instances of prior art, this intervention takes the form of additional DTMF sequences which maybe stored as a part of the dialing sequence used by the caller's equipment or entered by the caller manually. This requires either the caller have prior knowledge of the DTMF sequence required by the receiving device or the receiving device query the caller for the DTMF sequence. In another example, the voice caller must respond vocally to a stored query so that a voice signal detection circuit in the receiving equipment can identify a voice call. This intrusive method fails when the caller pauses sufficiently, as can happen with a PBX operator momentarily on hold, or with a speaker unfamiliar with the selected language of the stored message. In instances of prior art where carrier signals are placed on the subscriber line to query the presence of a fax or data modem, the methodology used is intrusive to voice callers.
Examples of relevant prior art, all of which contain one or more of the above limitations, are U.S. Pat. No. 4,660,218 to Hashimoto (1987), U.S. Pat. No. 4,821,312 to Horton et. Al. (1989), U.S. Pat. No. 4,852,153 to Streck (1989), U.S. Pat. No. 4,856,049 to Streck (1989), U.S. Pat. No. 4,879,741 to Liu (1989), U.S. Pat. No. 4,910,764 to Bowen (1990), U.S. Pat. No. 5,022,071 to Mozer et. al. (1991), U.S. Pat. No. 5,056,132 to Coleman et. Al. (1991), U.S. Pat. No. 5,065,427 to Godbole (1991), U.S. Pat. No. 5,146,489 to Telibasa (1992), U.S. Pat. No. 5,151,972 to Lorenz et. Al. (1992), and U.S. Pat. No. 5,187,736 to Moriizumi (1993).